Methods and systems for detecting and managing amplifier instability

ABSTRACT

A system may include a first input for receiving a first signal for driving an amplifier that drives a load, a second input for receiving a second signal driven by the amplifier, and an instability detector for detecting instability of a feedback loop for controlling the first signal based on comparison of the first signal and the second signal.

RELATED APPLICATION

The present disclosure claims priority to U.S. Provisional PatentApplication Ser. No. 62/944,426, filed Dec. 6, 2019, which isincorporated by reference herein in its entirety.

FIELD OF DISCLOSURE

The present disclosure relates in general to detecting instability in anamplifier, such as an amplifier used to drive a haptic vibrational load,and the management of such instability.

BACKGROUND

Vibro-haptic transducers, for example linear resonant actuators (LRAs),are widely used in portable devices such as mobile phones to generatevibrational feedback to a user. Vibro-haptic feedback in various formscreates different feelings of touch to a user's skin, and may playincreasing roles in human-machine interactions for modern devices.

An LRA may be modelled as a mass-spring electro-mechanical vibrationsystem. When driven with appropriately designed or controlled drivingsignals, an LRA may generate certain desired forms of vibrations. Forexample, a sharp and clear-cut vibration pattern on a user's finger maybe used to create a sensation that mimics a mechanical button click.This clear-cut vibration may then be used as a virtual switch to replacemechanical buttons.

FIG. 1 illustrates an example of a vibro-haptic system in a device 100.Device 100 may comprise a controller 101 configured to control a signalapplied to an amplifier 102. Amplifier 102 may then drive a haptictransducer 103 based on the signal. Controller 101 may be triggered by atrigger to output to the signal. The trigger may for example comprise apressure or force sensor on a screen or virtual button of device 100.

Among the various forms of vibro-haptic feedback, tonal vibrations ofsustained duration may play an important role to notify the user of thedevice of certain predefined events, such as incoming calls or messages,emergency alerts, and timer warnings, etc. In order to generate tonalvibration notifications efficiently, it may be desirable to operate thehaptic actuator at its resonance frequency.

The resonance frequency f₀ of a haptic transducer may be approximatelyestimated as:

$\begin{matrix}{f_{0} = \frac{1}{2*\pi*\sqrt{C*M}}} & (1)\end{matrix}$

where C is the compliance of the spring system, and M is the equivalentmoving mass, which may be determined based on both the actual movingpart in the haptic transducer and the mass of the portable deviceholding the haptic transducer.

Due to sample-to-sample variations in individual haptic transducers,mobile device assembly variations, temporal component changes caused byaging, component changes caused by self-heating, and use conditions suchas various different strengths of a user gripping of the device, thevibration resonance of the haptic transducer may vary from time to time.

FIG. 2A illustrates an example of a linear resonant actuator (LRA)modelled as a linear system including a mass-spring system 201. LRAs arenon-linear components that may behave differently depending on, forexample, the voltage levels applied, the operating temperature, and thefrequency of operation. However, these components may be modelled aslinear components within certain conditions.

FIG. 2B illustrates an example of an LRA modelled as a linear system,including an electrically equivalent model of mass-spring system 201 ofLRA. In this example, the LRA is modelled as a third order system havingelectrical and mechanical elements. In particular, Re and Le are the DCresistance and coil inductance of the coil-magnet system, respectively;and Bl is the magnetic force factor of the coil. The driving amplifieroutputs the voltage waveform V(t) with the output impedance Ro. Theterminal voltage V_(T) (t) may be sensed across the terminals of thehaptic transducer. The mass-spring system 201 moves with velocity u(t).

An electromagnetic load such as an LRA may be characterized by itsimpedance Z_(LRA) as seen as the sum of a coil impedance Z_(coil) and amechanical impedance Z_(mech):

Z _(LRA) =Z _(coil) +Z _(mech)   (2)

Coil impedance Z_(coil) may in turn comprise a direct current (DC)resistance Re in series with an inductance Le:

Z _(coil) =Re+s*Le   (3)

Mechanical impedance Z_(mech) may be defined by three parametersincluding the resistance at resonance R_(RES) representing an electricalresistance representative of mechanical friction of the mass-springsystem of the haptic transducer, a capacitance C_(MES) representing anelectrical capacitance representative of an equivalent moving mass M ofthe mass-spring system of the haptic transducer, and inductance L_(CES)representative of a compliance C of the mass-spring system of the haptictransducer. The electrical equivalent of the total mechanical impedanceis the parallel connection of R_(RES), C_(MES), L_(CES). The Laplacetransform of this parallel connection is described by:

$\begin{matrix}{{Z_{mech}(s)} = \frac{1}{\left( {\frac{1}{R_{RES}} + \frac{1}{L_{CES}*s} + {C_{MES}*s}} \right)}} & (4)\end{matrix}$

The resonant frequency f₀ of the haptic transducer can be representedas:

$\begin{matrix}{f_{0} = \frac{1}{\left( {2*\pi*\sqrt{L_{CES}*C_{MES}*}} \right)}} & (5)\end{matrix}$

The quality factor Q of the LRA can be represented as:

$\begin{matrix}{Q = {\frac{R_{RES} + {Re}}{R_{RES} + {Re}}*\sqrt{\frac{C_{MES}}{L_{CES}}}}} & (6)\end{matrix}$

Referring to equation (6), it may appear non-intuitive that theexpression involves a subexpression describing the parallel connectionof resistances Re and

$R_{RES}\mspace{14mu} \left( {{i.e.},\frac{R_{RES}*{Re}}{R_{RES} + {Re}}} \right)$

while in FIG. 2B these resistances are shown in a series connection.However, such may be the case where a driving voltage Ve is oscillatingbut then abruptly turns off and goes to zero. The voltage amplifiershown in FIGURE 2B may be considered to have a low source impedance,ideally zero source impedance. Under these conditions, when drivingvoltage Ve goes to zero, the voltage amplifier effectively disappearsfrom the circuit. At that point, the top-most terminal of resistance Rein FIG. 2B is grounded as is the bottom-most terminal of resistanceR_(RES) and so resistances Re and R_(RES) are indeed connected inparallel as reflected in equation (6).

Electromagnetic transducers, such as LRAs or microspeakers, may haveslow response times. FIG. 3 is a graph of an example response of an LRA,depicting an example driving signal to the LRA, a current through theLRA, and a back electromotive force (back EMF) of the LRA, wherein suchback EMF may be proportional to the velocity of a moving element (e.g.,coil or magnet) of the transducer. As shown in FIG. 3, the attack timeof the back EMF may be slow as energy is transferred to the LRA, andsome “ringing” of the back EMF may occur after the driving signal hasended as the mechanical energy stored in the LRA is discharged. In thecontext of a haptic LRA, such behavioral characteristic may result in a“mushy” feeling click or pulse, instead of a “crisp” tactile response.Thus, it may be desirable for an LRA to instead have a response similarto that shown in FIG. 4, in which there exists minimal ringing after thedriving signal has ended, and which may provide a more “crisp” tactileresponse in a haptic context. Accordingly, it may be desirable to applyprocessing to a driving signal such that when the processed drivingsignal is applied to the transducer, the velocity or back EMF of thetransducer more closely approaches that of FIG. 4.

SUMMARY

In accordance with the teachings of the present disclosure, thedisadvantages and problems associated with detecting and managinginstability in an amplifier may be reduced or eliminated.

In accordance with embodiments of the present disclosure, a method mayinclude receiving a first signal for driving an amplifier that drives aload, receiving a second signal driven by the amplifier, and detectinginstability of a feedback loop for controlling the first signal based oncomparison of the first signal and the second signal.

In accordance with these and other embodiments of the presentdisclosure, a system may include a first input for receiving a firstsignal for driving an amplifier that drives a load, a second input forreceiving a second signal driven by the amplifier, and an instabilitydetector for detecting instability of a feedback loop for controllingthe first signal based on comparison of the first signal and the secondsignal.

In accordance with these and other embodiments of the presentdisclosure, a host device may include an amplifier that drives a loadand a processing subsystem comprising a first input for receiving afirst signal for driving an amplifier that drives a load, a second inputfor receiving a second signal driven by the amplifier, and aninstability detector for detecting instability of a feedback loop forcontrolling the first signal based on comparison of the first signal andthe second signal.

Technical advantages of the present disclosure may be readily apparentto one having ordinary skill in the art from the figures, descriptionand claims included herein. The objects and advantages of theembodiments will be realized and achieved at least by the elements,features, and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are examples and explanatory and arenot restrictive of the claims set forth in this disclosure.

“Intentionaly Left Blank”

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like referencenumbers indicate like features, and wherein:

FIG. 1 illustrates an example of a vibro-haptic system in a device, asis known in the art;

FIGS. 2A and 2B each illustrate an example of a Linear Resonant Actuator(LRA) modelled as a linear system, as is known in the art;

FIG. 3 illustrates a graph of example waveforms of an electromagneticload, as is known in the art;

FIG. 4 illustrates a graph of desirable example waveforms of anelectromagnetic load, in accordance with embodiments of the presentdisclosure;

FIG. 5 illustrates a block diagram of selected components of an examplemobile device, in accordance with embodiments of the present disclosure;

FIG. 6 illustrates a block diagram of selected components of an exampleintegrated haptic system, in accordance with embodiments of the presentdisclosure;

FIG. 7 illustrates an example system for improving transducer dynamics,in accordance with embodiments of the present disclosure;

FIG. 8 illustrates an example of a linear resonant actuator (LRA)modelled as a linear system and including a negative resistance, inaccordance with embodiments of the present disclosure; and

FIG. 9 illustrates a block diagram of selected components of an exampleinstability detector, in accordance with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The description below sets forth example embodiments according to thisdisclosure. Further example embodiments and implementations will beapparent to those having ordinary skill in the art. Further, thosehaving ordinary skill in the art will recognize that various equivalenttechniques may be applied in lieu of, or in conjunction with, theembodiment discussed below, and all such equivalents should be deemed asbeing encompassed by the present disclosure.

Various electronic devices or smart devices may have transducers,speakers, and acoustic output transducers, for example any transducerfor converting a suitable electrical driving signal into an acousticoutput such as a sonic pressure wave or mechanical vibration. Forexample, many electronic devices may include one or more speakers orloudspeakers for sound generation, for example, for playback of audiocontent, voice communications and/or for providing audiblenotifications.

Such speakers or loudspeakers may comprise an electromagnetic actuator,for example a voice coil motor, which is mechanically coupled to aflexible diaphragm, for example a conventional loudspeaker cone, orwhich is mechanically coupled to a surface of a device, for example theglass screen of a mobile device. Some electronic devices may alsoinclude acoustic output transducers capable of generating ultrasonicwaves, for example for use in proximity detection type applicationsand/or machine-to-machine communication.

Many electronic devices may additionally or alternatively include morespecialized acoustic output transducers, for example, haptictransducers, tailored for generating vibrations for haptic controlfeedback or notifications to a user. Additionally or alternatively, anelectronic device may have a connector, e.g., a socket, for making aremovable mating connection with a corresponding connector of anaccessory apparatus, and may be arranged to provide a driving signal tothe connector so as to drive a transducer, of one or more of the typesmentioned above, of the accessory apparatus when connected. Such anelectronic device will thus comprise driving circuitry for driving thetransducer of the host device or connected accessory with a suitabledriving signal. For acoustic or haptic transducers, the driving signalwill generally be an analog time varying voltage signal, for example, atime varying waveform.

FIG. 5 illustrates a block diagram of selected components of an examplehost device 502, in accordance with embodiments of the presentdisclosure. As shown in FIG. 5, host device 502 may comprise anenclosure 501, a controller 503, a memory 504, a force sensor 505, amicrophone 506, a linear resonant actuator 507, a radiotransmitter/receiver 508, a speaker 510, and an integrated haptic system512.

Enclosure 501 may comprise any suitable housing, casing, or otherenclosure for housing the various components of host device 502.Enclosure 501 may be constructed from plastic, metal, and/or any othersuitable materials. In addition, enclosure 501 may be adapted (e.g.,sized and shaped) such that host device 502 is readily transported on aperson of a user of host device 502. Accordingly, host device 502 mayinclude but is not limited to a smart phone, a tablet computing device,a handheld computing device, a personal digital assistant, a notebookcomputer, a video game controller, or any other device that may bereadily transported on a person of a user of host device 502.

Controller 503 may be housed within enclosure 501 and may include anysystem, device, or apparatus configured to interpret and/or executeprogram instructions and/or process data, and may include, withoutlimitation a microprocessor, microcontroller, digital signal processor(DSP), application specific integrated circuit (ASIC), or any otherdigital or analog circuitry configured to interpret and/or executeprogram instructions and/or process data. In some embodiments,controller 503 interprets and/or executes program instructions and/orprocesses data stored in memory 504 and/or other computer-readable mediaaccessible to controller 503.

Memory 504 may be housed within enclosure 501, may be communicativelycoupled to controller 503, and may include any system, device, orapparatus configured to retain program instructions and/or data for aperiod of time (e.g., computer-readable media). Memory 504 may includerandom access memory (RAM), electrically erasable programmable read-onlymemory (EEPROM), a Personal Computer Memory Card InternationalAssociation (PCMCIA) card, flash memory, magnetic storage, opto-magneticstorage, or any suitable selection and/or array of volatile ornon-volatile memory that retains data after power to host device 502 isturned off.

Microphone 506 may be housed at least partially within enclosure 501,may be communicatively coupled to controller 503, and may comprise anysystem, device, or apparatus configured to convert sound incident atmicrophone 506 to an electrical signal that may be processed bycontroller 503, wherein such sound is converted to an electrical signalusing a diaphragm or membrane having an electrical capacitance thatvaries as based on sonic vibrations received at the diaphragm ormembrane. Microphone 506 may include an electrostatic microphone, acondenser microphone, an electret microphone, a microelectromechanicalsystems (MEMs) microphone, or any other suitable capacitive microphone.

Radio transmitter/receiver 508 may be housed within enclosure 501, maybe communicatively coupled to controller 503, and may include anysystem, device, or apparatus configured to, with the aid of an antenna,generate and transmit radio-frequency signals as well as receiveradio-frequency signals and convert the information carried by suchreceived signals into a form usable by controller 503. Radiotransmitter/receiver 508 may be configured to transmit and/or receivevarious types of radio-frequency signals, including without limitation,cellular communications (e.g., 2G, 3G, 4G, LTE, etc.), short-rangewireless communications (e.g., BLUETOOTH), commercial radio signals,television signals, satellite radio signals (e.g., GPS), WirelessFidelity, etc.

A speaker 510 may be housed at least partially within enclosure 501 ormay be external to enclosure 501, may be communicatively coupled tocontroller 503, and may comprise any system, device, or apparatusconfigured to produce sound in response to electrical audio signalinput. In some embodiments, a speaker may comprise a dynamicloudspeaker, which employs a lightweight diaphragm mechanically coupledto a rigid frame via a flexible suspension that constrains a voice coilto move axially through a cylindrical magnetic gap. When an electricalsignal is applied to the voice coil, a magnetic field is created by theelectric current in the voice coil, making it a variable electromagnet.The coil and the driver's magnetic system interact, generating amechanical force that causes the coil (and thus, the attached cone) tomove back and forth, thereby reproducing sound under the control of theapplied electrical signal coming from the amplifier.

Force sensor 505 may be housed within enclosure 501, and may include anysuitable system, device, or apparatus for sensing a force, a pressure,or a touch (e.g., an interaction with a human finger) and generating anelectrical or electronic signal in response to such force, pressure, ortouch. In some embodiments, such electrical or electronic signal may bea function of a magnitude of the force, pressure, or touch applied tothe force sensor. In these and other embodiments, such electronic orelectrical signal may comprise a general purpose input/output signal(GPIO) associated with an input signal to which haptic feedback isgiven. Force sensor 505 may include, without limitation, a capacitivedisplacement sensor, an inductive force sensor (e.g., aresistive-inductive-capacitive sensor), a strain gauge, a piezoelectricforce sensor, force sensing resistor, piezoelectric force sensor, thinfilm force sensor, or a quantum tunneling composite-based force sensor.For purposes of clarity and exposition in this disclosure, the term“force” as used herein may refer not only to force, but to physicalquantities indicative of force or analogous to force, such as, but notlimited to, pressure and touch.

Linear resonant actuator 507 may be housed within enclosure 501, and mayinclude any suitable system, device, or apparatus for producing anoscillating mechanical force across a single axis. For example, in someembodiments, linear resonant actuator 507 may rely on an alternatingcurrent voltage to drive a voice coil pressed against a moving massconnected to a spring. When the voice coil is driven at the resonantfrequency of the spring, linear resonant actuator 507 may vibrate with aperceptible force. Thus, linear resonant actuator 507 may be useful inhaptic applications within a specific frequency range. While, for thepurposes of clarity and exposition, this disclosure is described inrelation to the use of linear resonant actuator 507, it is understoodthat any other type or types of vibrational actuators (e.g., eccentricrotating mass actuators) may be used in lieu of or in addition to linearresonant actuator 507. In addition, it is also understood that actuatorsarranged to produce an oscillating mechanical force across multiple axesmay be used in lieu of or in addition to linear resonant actuator 507.As described elsewhere in this disclosure, a linear resonant actuator507, based on a signal received from integrated haptic system 512, mayrender haptic feedback to a user of host device 502 for at least one ofmechanical button replacement and capacitive sensor feedback.

Integrated haptic system 512 may be housed within enclosure 501, may becommunicatively coupled to force sensor 505 and linear resonant actuator507, and may include any system, device, or apparatus configured toreceive a signal from force sensor 505 indicative of a force applied tohost device 502 (e.g., a force applied by a human finger to a virtualbutton of host device 502) and generate an electronic signal for drivinglinear resonant actuator 507 in response to the force applied to hostdevice 502. Detail of an example integrated haptic system in accordancewith embodiments of the present disclosure is depicted in FIG. 6.

Although specific example components are depicted above in FIG. 5 asbeing integral to host device 502 (e.g., controller 503, memory 504,force sensor 506, microphone 506, radio transmitter/receiver 508,speakers(s) 510), a host device 502 in accordance with this disclosuremay comprise one or more components not specifically enumerated above.For example, although FIG. 5 depicts certain user interface components,host device 502 may include one or more other user interface componentsin addition to those depicted in FIG. 5 (including but not limited to akeypad, a touch screen, and a display), thus allowing a user to interactwith and/or otherwise manipulate host device 502 and its associatedcomponents.

FIG. 6 illustrates a block diagram of selected components of an exampleintegrated haptic system 512A, in accordance with embodiments of thepresent disclosure. In some embodiments, integrated haptic system 512Amay be used to implement integrated haptic system 512 of FIG. 5. Asshown in FIG. 6, integrated haptic system 512A may include a digitalsignal processor (DSP) 602, a memory 604, and an amplifier 606.

DSP 602 may include any system, device, or apparatus configured tointerpret and/or execute program instructions and/or process data. Insome embodiments, DSP 602 may interpret and/or execute programinstructions and/or process data stored in memory 604 and/or othercomputer-readable media accessible to DSP 602.

Memory 604 may be communicatively coupled to DSP 602, and may includeany system, device, or apparatus configured to retain programinstructions and/or data for a period of time (e.g., computer-readablemedia). Memory 604 may include random access memory (RAM), electricallyerasable programmable read-only memory (EEPROM), a Personal ComputerMemory Card International Association (PCMCIA) card, flash memory,magnetic storage, opto-magnetic storage, or any suitable selectionand/or array of volatile or non-volatile memory that retains data afterpower to host device 502 is turned off.

Amplifier 606 may be electrically coupled to DSP 602 and may compriseany suitable electronic system, device, or apparatus configured toincrease the power of an input signal V_(IN) (e.g., a time-varyingvoltage or current) to generate an output signal V_(OUT). For example,amplifier 606 may use electric power from a power supply (not explicitlyshown) to increase the amplitude of a signal. Amplifier 606 may includeany suitable amplifier class, including without limitation, a Class-Damplifier.

In operation, memory 604 may store one or more haptic playbackwaveforms. In some embodiments, each of the one or more haptic playbackwaveforms may define a haptic response a(t) as a desired acceleration ofa linear resonant actuator (e.g., linear resonant actuator 507) as afunction of time. DSP 602 may be configured to receive a force signalV_(SENSE) indicative of force applied to force sensor 505. Either inresponse to receipt of force signal VSENSE indicating a sensed force orindependently of such receipt, DSP 602 may retrieve a haptic playbackwaveform from memory 604 and process such haptic playback waveform todetermine a processed haptic playback signal V_(IN). In embodiments inwhich amplifier 606 is a Class D amplifier, processed haptic playbacksignal V_(IN) may comprise a pulse-width modulated signal. In responseto receipt of force signal V_(SENSE) indicating a sensed force, DSP 602may cause processed haptic playback signal V_(IN) to be output toamplifier 606, and amplifier 606 may amplify processed haptic playbacksignal V_(IN) to generate a haptic output signal V_(OUT) for drivinglinear resonant actuator 507.

In some embodiments, integrated haptic system 512A may be formed on asingle integrated circuit, thus enabling lower latency than existingapproaches to haptic feedback control. By providing integrated hapticsystem 512A as part of a single monolithic integrated circuit, latenciesbetween various interfaces and system components of integrated hapticsystem 512A may be reduced or eliminated.

The problem illustrated in FIG. 3 may result from a linear resonantactuator 507 with a high quality factor q with a sharp peak in impedanceat a resonant frequency f₀ of linear resonant actuator 507.

FIG. 7 illustrates an example system 700 for improving dynamics of anelectromagnetic load 701, in accordance with embodiments of the presentdisclosure. In some embodiments, system 700 may be integral to a hostdevice (e.g., host device 502) comprising system 700 and electromagneticload 701.

In operation, a pulse generator 722 of a system 700 of a host device maygenerate a raw transducer driving signal x′ (t) (which, in someembodiments, may be a waveform signal, such as a haptic waveform signalor audio signal). In some embodiments, raw transducer driving signal x′(t) may be generated based on a desired playback waveform received bypulse generator 722.

Raw transducer driving signal x′ (t) may be received by negativeimpedance filter 726 which, as described in greater detail below, may beapplied to raw transducer driving signal x′ (t) to reduce an effectivequality factor q of the electromagnetic load 701, which may in turndecrease attack time and minimize ringing occurring after the rawtransducer driving signal has ended, thus generating transducer drivingsignal x(t) to the output of negative impedance filter 726.

Transducer driving signal x (t) may in turn be amplified by amplifier706 to generate a driving signal V(t) for driving electromagnetic load701. Responsive to driving signal V(t), a sensed terminal voltage V_(T)(t) of electromagnetic load 701 may be converted to a digitalrepresentation by a first analog-to-digital converter (ADC) 703.Similarly, sensed current I(t) may be converted to a digitalrepresentation by a second ADC 704. Current I(t) may be sensed across ashunt resistor 702 having resistance R_(s) coupled to a terminal ofelectromagnetic load 701. The terminal voltage V_(T)(t) may be sensed bya terminal voltage sensing block 707, for example a volt meter.

As shown in FIG. 7, system 700 may include an impedance estimator 710.Impedance estimator 710 may include any suitable system, device, orapparatus configured to estimate, based on sensed terminal voltageV_(T)(t), sensed current I(t), and/or any other measured parameters ofelectromagnetic load 701, one or more components of the electricaland/or mechanical impedances of electromagnetic load 701, and generateone or more control signals (e.g., a negative impedance Re_neg) forcontrolling a response of negative impedance filter 726. Examples ofapproaches for estimating one or more components of the electricaland/or mechanical impedances of electromagnetic load 701 and generatinga negative impedance value Re_neg are described in, without limitation,U.S. patent application Ser. No. 16/816,790 filed Mar. 12, 2020 andentitled “Methods and Systems for Improving Transducer Dynamics;” U.S.patent application Ser. No. 16/816,833 filed Mar. 12, 2020 and entitled“Methods and Systems for Estimating Transducer Parameters;” U.S. patentapplication Ser. No. 16/842,482 filed Apr. 7, 2020 and entitled “ThermalModel of Transducer for Thermal Protection and Resistance Estimation;”and U.S. patent application Ser. No. 16/369,556 filed Mar. 29, 2019 andentitled “Driver Circuitry;”

all of which is incorporated by reference herein in their entireties.

As mentioned above and described in greater detail below, a system 700may implement negative impedance filter 726 to apply to the rawtransducer driving signal, which may reduce an effective quality factorq of the transducer, which may in turn decrease attack time and minimizeringing occurring after the raw transducer driving signal has ended.Quality factor q of a transducer may be expressed as:

$\begin{matrix}{q = {\frac{R_{RES}*{Re}}{R_{RES} + {Re}}*\sqrt{\frac{C_{MES}}{L_{CES}}}}} & (7)\end{matrix}$

In equation (7), as DC resistance Re increases, the numerator termR_(RES)* Re increases more rapidly than the denominator term R_(RES)+Re.Therefore, quality factor q generally increases with increasing DCresistance Re. Accordingly, one way system 700 may minimize qualityfactor q is to effectively decrease DC resistance Re. In someembodiments, system 700 may ideally decrease the effective DC resistanceRe to a point in which critical damping occurs in electromagnetic load701.

Turning briefly to FIG. 8, FIG. 8 illustrates an example of haptictransducer 701 modelled as a linear system including electricalcomponents 802 and electrical model of mechanical components 804 andincluding a negative resistance resistor 806 with negative impedanceRe_neg inserted in series with haptic transducer 701, in accordance withembodiments of the present disclosure. The addition of negativeimpedance Re_neg may lower quality factor q because effectively itsubtracts from DC resistance Re thereby reducing the overall DCelectrical impedance.

In practice, negative resistors do not exist. Instead, negativeimpedance filter 726 may comprise a digital filter configured to behavesubstantially like the circuit shown in FIG. 8, including a mathematicalmodel of negative impedance Re_neg in series with a mathematical modelof haptic transducer 701. In operation, negative impedance filter 726may in effect compute a voltage V_(m) that would occur at the junctionof negative impedance Re_neg and DC resistance Re as shown in FIG. 8,if, in fact, it were possible to place a physical resistor with negativeimpedance Re_neg in series with haptic transducer 701. Computed voltageV_(m) may then be used to drive haptic transducer 701.

In essence, system 700 implements a sensorless velocity control feedbackloop for electromagnetic load 701. The feedback loop may use a dynamicestimate of parameters of electromagnetic load 701 and generate feedback(e.g., negative impedance Re_neg and the response of negative impedancefilter 726) to cancel most of the electrical and mechanical impedance ofelectromagnetic load 701. The electrical and mechanical impedance ofelectromagnetic load 701 may change in response to the stimulus appliedto it (e.g., amplitude and frequency of driving signal V(t)), ambienttemperature conditions, and/or other factors.

In order for impedance cancellation performed by the feedback loop to beeffective, most of the impedance of electromagnetic load 701 should becancelled (e.g., from 95% to just under 100% of the impedance ofelectromagnetic load 701). However, when the feedback loop cancelsalmost all of the impedance of electromagnetic load 701, instability ofthe feedback loop may result, for example if the impedance to becancelled is incorrectly estimated.

Thus, turning back to FIG. 7, to balance the effectiveness of reducingquality factor q with prevention of instability in the feedback loop,system 700 may include an instability detector 712 to detect instabilityand, when instability is detected, reduce (at least temporarily) theamount of the impedance of electromagnetic load 701 cancelled in orderto prevent instability.

In the feedback loop depicted in FIG. 7, instability may be defined as acondition in which output to electromagnetic load 701, which may beindicated by sensed terminal voltage V_(T)(t), does not correlate withraw transducer driving signal x′(t). Accordingly, instability detector712 may receive sensed terminal voltage V_(T)(t) and raw transducerdriving signal x′(t) as inputs, although in some embodiments instabilitydetector 712 may monitor sensed current I(t) in addition to or in lieuof sensed terminal voltage V_(T)(t).

FIG. 9 illustrates a block diagram of selected components of an exampleinstability detector 712, in accordance with embodiments of the presentdisclosure. As shown in FIG. 9, instability detector 712 may receivesensed terminal voltage V_(T)(t) and raw transducer driving signal x′(t)and apply a Hilbert transform 902 (or any other suitable transform withsimilar functionality) to generate analytic signals having both real andimaginary components of sensed terminal voltage V_(T)(t) and rawtransducer driving signal x′(t). Conjugate multiplier 904 may conjugatethese real and imaginary components to obtain a phase angle thatrepresents a phase angle difference between sensed terminal voltageV_(T)(t) and raw transducer driving signal x′(t). The signal output byconjugate multiplier 904 may be filtered by high-pass filter 906 toremove direct-current components, leaving a phase angle Δφ representingthe phase difference between sensed terminal voltage V_(T)(t) and rawtransducer driving signal x′ (t). Absolute value block 908 may receivephase angle Δφ and output phase angle magnitude |Δφ|. A comparator 910may compare phase angle magnitude |Δφ| to a threshold value. Based onthe comparison performed by comparator 910, a multiplexer 912 may selecta gain GAIN (e.g., to be applied to negative impedance Re_neg by a gainelement 714 of FIG. 7). For example, when phase angle magnitude |Δφ| isbelow the threshold value, multiplexer 912 may select a higher gain HI,but when phase angle magnitude |Δφ| is above the threshold value,multiplexer 912 may select a lower gain LO.

Although the foregoing contemplates instability control by controlling again applied to negative impedance Re_neg, in some embodiments,instability detector 712 may control other parameters in order tomaintain feedback loop stability. For example, in addition to or in lieuof controlling a gain applied to negative impedance Re_neg, in someembodiments, instability detector 712 may control a response of negativeimpedance filter 726, operational parameters of amplifier 706, and/orany other parameters of system 700.

Although the foregoing discusses application to a linear electromagneticload, it is understood that systems and methods similar or identical tothose disclosed may be applied to other linear or non-linear systems.

Further, although the foregoing contemplates use of a negativeresistance filter to implement a model of an LRA, in some embodiments amathematical equivalent to an LRA may be used in lieu of a model.

As used herein, when two or more elements are referred to as “coupled”to one another, such term indicates that such two or more elements arein electronic communication or mechanical communication, as applicable,whether connected indirectly or directly, with or without interveningelements.

This disclosure encompasses all changes, substitutions, variations,alterations, and modifications to the example embodiments herein that aperson having ordinary skill in the art would comprehend. Similarly,where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend. Moreover, reference in the appended claims to an apparatusor system or a component of an apparatus or system being adapted to,arranged to, capable of, configured to, enabled to, operable to, oroperative to perform a particular function encompasses that apparatus,system, or component, whether or not it or that particular function isactivated, turned on, or unlocked, as long as that apparatus, system, orcomponent is so adapted, arranged, capable, configured, enabled,operable, or operative. Accordingly, modifications, additions, oromissions may be made to the systems, apparatuses, and methods describedherein without departing from the scope of the disclosure. For example,the components of the systems and apparatuses may be integrated orseparated. Moreover, the operations of the systems and apparatusesdisclosed herein may be performed by more, fewer, or other componentsand the methods described may include more, fewer, or other steps.Additionally, steps may be performed in any suitable order. As used inthis document, “each” refers to each member of a set or each member of asubset of a set.

Although exemplary embodiments are illustrated in the figures anddescribed below, the principles of the present disclosure may beimplemented using any number of techniques, whether currently known ornot. The present disclosure should in no way be limited to the exemplaryimplementations and techniques illustrated in the drawings and describedabove.

Unless otherwise specifically noted, articles depicted in the drawingsare not necessarily drawn to scale.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the disclosureand the concepts contributed by the inventor to furthering the art, andare construed as being without limitation to such specifically recitedexamples and conditions. Although embodiments of the present disclosurehave been described in detail, it should be understood that variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the disclosure.

Although specific advantages have been enumerated above, variousembodiments may include some, none, or all of the enumerated advantages.Additionally, other technical advantages may become readily apparent toone of ordinary skill in the art after review of the foregoing figuresand description.

To aid the Patent Office and any readers of any patent issued on thisapplication in interpreting the claims appended hereto, applicants wishto note that they do not intend any of the appended claims or claimelements to invoke 35 U.S.C. § 112(f) unless the words “means for” or“step for” are explicitly used in the particular claim.

What is claimed is:
 1. A method comprising: receiving a first signal fordriving an amplifier that drives a load; receiving a second signaldriven by the amplifier; and detecting instability of a feedback loopfor controlling the first signal based on comparison of the first signaland the second signal.
 2. The method of claim 1, wherein the load is ahaptic transducer.
 3. The method of claim 1, wherein the comparison ofthe first signal and the second signal comprises comparing a phasedifference between respective phase angles of the first signal and thesecond signal.
 4. The method of claim 3, further comprising: performinga first transform of the first signal into real and imaginarycomponents; and performing a second transform of the second signal intoreal and imaginary components.
 5. The method of claim 4, wherein each ofthe first transform and the second transform comprises a Hilberttransform.
 6. The method of claim 4, further comprising performing aconjugate multiplication of the respective real and imaginary componentsof the first signal and the second signal to generate the phasedifference.
 7. The method of claim 1, further comprising modifying thefirst signal responsive to determining instability of the feedback loop.8. The method of claim 1, further comprising modifying a gain of thefeedback loop responsive to determining instability of the feedbackloop.
 9. The method of claim 1, wherein a component of the feedback loopmodels a virtual negative impedance to be virtually applied to at leastpartially offset impedance of the load, and the method further comprisesmodifying the virtual negative impedance responsive to determininginstability of the feedback loop.
 10. The method of claim 1, wherein theload comprises an electromagnetic load.
 11. A system comprising: a firstinput for receiving a first signal for driving an amplifier that drivesa load; a second input for receiving a second signal driven by theamplifier; and an instability detector for detecting instability of afeedback loop for controlling the first signal based on comparison ofthe first signal and the second signal.
 12. The system of claim 11,wherein the load is a haptic transducer.
 13. The system of claim 11,wherein the comparison of the first signal and the second signalcomprises comparing a phase difference between respective phase anglesof the first signal and the second signal.
 14. The system of claim 13,wherein the instability detector is further configured to: perform afirst transform of the first signal into real and imaginary components;and perform a second transform of the second signal into real andimaginary components.
 15. The system of claim 14, wherein each of thefirst transform and the second transform comprises a Hilbert transform.16. The system of claim 14, wherein the instability detector is furtherconfigured to perform a conjugate multiplication of the respective realand imaginary components of the first signal and the second signal togenerate the phase difference.
 17. The system of claim 11, wherein theinstability detector is further configured to cause modification of thefirst signal responsive to determining instability of the feedback loop.18. The system of claim 11, wherein the instability detector is furtherconfigured to cause modification of a gain of the feedback loopresponsive to determining instability of the feedback loop.
 19. Thesystem of claim 11, wherein a component of the feedback loop models avirtual negative impedance to be virtually applied to at least partiallyoffset impedance of the load, and the method further comprises modifyingthe virtual negative impedance responsive to determining instability ofthe feedback loop.
 20. The system of claim 11, wherein the loadcomprises an electromagnetic load.
 21. A host device comprising: anamplifier that drives a load; and a processing subsystem comprising: afirst input for receiving a first signal for driving an amplifier thatdrives a load; a second input for receiving a second signal driven bythe amplifier; and an instability detector for detecting instability ofa feedback loop for controlling the first signal based on comparison ofthe first signal and the second signal.